The invention relates to a feed device intended for feeding fuel out of a fuel tank to an internal combustion engine of a motor vehicle, with a feed pump and with means for controlling a pressure within a forward-flow line led from the feed pump to the internal combustion engine.
Such a feed device has as means for controlling the pressure a throttle arranged between the forward-flow line and a return-flow line led back from the internal combustion engine to the fuel tank and is known from practice. Controlling the pressure of the forward-flow line is intended to ensure that a high pressure prevails in the forward-flow line with the internal combustion engine having a high power consumption and a low pressure prevailing there during starting. Furthermore, in the case of high volume flows, pressure losses occur within the lines and are to be compensated by means of the control.
A disadvantage of the known feed device is that, particularly when the internal combustion engine is in the high-load range, the throttle often cannot reliably maintain an intended high pressure in the forward-flow line, since fuel overflows from the forward-flow line via the throttle into the return-flow line which has a low pressure.
The problem on which the invention is based is to design a feed device of the type initially mentioned, in such a way that it makes it possible to maintain the pressure within the forward-flow line with particularly high accuracy.
This problem is solved, according to the invention, in that the forward-flow line has a pressure regulating valve capable of being activated by the pressure within the return-flow line, and in that the pressure regulating valve is designed for closing or opening a branch leading from the forward-flow line into the fuel tank.
By virtue of this design of the feed device according to the invention, the power-dependent and rotational-speed-dependent pressure in the return-flow line is utilized in order to set the operating point of the pressure regulating valve. Since the pressure in it the return-flow line is dependent on the load state of the internal combustion engine, the pressure in the forward-flow line can thereby be regulated with very high accuracy. In the case of a particularly high fuel requirement, the pressure regulating valve can close the connection to the branch completely, so that the entire fuel fed by the feed pump arrives at the internal combustion engine.
A suction jet pump connected via a branch to the forward-flow line and provided for feeding fuel out of one chamber into another chamber is usually arranged in the fuel tank. In this case, a feed of the suction jet pump can be reliably ensured if a mixer for mixing the fuel flowing back via the return-flow line with fuel branched off from the forward-flow line and intended for supplying a suction jet pump is arranged within the return-flow line. Moreover, the suction jet pump generates a counterpressure in the return-flow line, so that the control of the pressure regulating valve and therefore the pressure regulated in the forward-flow line is particularly accurate. At the same time, by the pressure regulating valve being arranged according to the invention in the forward-flow line, it becomes possible, in the case of a high fuel consumption by the internal combustion engine or a low delivery of the feed pump, for a particularly small amount of fuel to flow out via the branch into the fuel tank.
When there is-a high pressure difference between the forward-flow line and return-flow line, a high pressure in the forward-flow line can be kept below an intended value if the mixer has a non-return valve which closes the return-flow line above an intended pressure difference between the fuel branched off from the forward-flow line and the fuel flowing back via the return-flow line. This design prevents the pressure regulating valve from being activated in the case of the high pressure difference, so that the pressure regulating valve is open and allows the fuel to flow out of the forward-flow line through the branch.
According to another advantageous development of the invention, an intended maximum pressure of the forward-flow line can be maintained particularly reliably if the forward-flow line is connected to a pressure limiting valve which opens above an intended pressure and which has a connection to the fuel tank.
According to another advantageous development of the invention, emissions of fuel into the environment can be kept particularly low if the pressure limiting valve, the pressure regulating valve and the nonreturn valve are intended to be arranged within the fuel tank. As a result, all the connections of the feed device according to the invention are arranged within the fuel tank, so that leaks do not lead to an escape of fuel.
The invention permits numerous embodiments. In order to make its basic principle even clearer, one of these is illustrated in the drawing and described below.